Excipients are added to pharmaceutical formulations to aid in the stabilization of the active compound. The compatibility of the excipients with the active compound is crucial for the quality and stability of the pharmaceutical formulation. While excipients are important in the stabilization of the active compound, excipients can cause problems: the excipient may degrade and thus lose its mechanism of stabilization or it may produce degradants that interact with the active compound.
Pharmaceutical formulations in which the active compound is a polypeptide, e.g. an antibody, can pose special problems as polypeptides generally are larger and more complex than traditional organic and inorganic molecules (for example, polypeptides possess multiple functional groups, in addition to complex three-dimensional structures). In addition, for a polypeptide to remain biologically active, the pharmaceutical polypeptide formulation must preserve intact the conformational integrity of at least a core sequence of the polypeptide's amino acids, while at the same time maintaining physical and chemical stability of the pharmaceutical polypeptide formulation. Excipients are generally stable in aqueous solution; however, excipients in a pharmaceutical polypeptide formulation can interact with the polypeptide to undergo degradation in a formulation and can prevent the stabilization of the protein or the degradants could interact with the polypeptide to pose challenges (such as a loss in activity). Therefore, the evaluation of the interaction of the non-active components of the pharmaceutical formulation and polypeptide active agent is crucial for ensuring chemical and physical stability.
Polysorbates are non-ionic surfactants used to stabilize an active compound against interface induced aggregation and surface adsorption. Polysorbates can be effective against various stresses such as agitation (for example, shaking or stirring), freeze/thawing, and lyophilization. In pharmaceutical polypeptide formulations, polysorbates minimize adsorption to surfaces and reduce the air-liquid interfacial surface tension and thus the rate of protein denaturation. Loss of polysorbate in the pharmaceutical formulation can result in instability of the formulation. Further, polysorbates can be degraded by oxidation and hydrolysis which can lead to a decrease in the apparent concentration of polysorbate in the pharmaceutical formulation over long shelf life. Polysorbates (e.g., polysorbate 20) can be cleaved to produce degradants (e.g., free lauric acid and sorbitan polyoxyethylene side chain). These polysorbate degradants are less surface-active than nondegraded polysorbate and hence the chemical and physical stability of the pharmaceutical formulation may be compromised. Further, some polysorbate degradants are insoluble and may form particles if they are not solubilized by intact polysorbate, i.e., if the ratio of degraded polysorbate 20:intact polysorbate 20 is too high.
The rate and extent of degradation of polysorbate is influenced by the chemical and physical properties of the active compound, and the stabilizing ability of polysorbate can vary between different pharmaceutical formulations comprising different active compounds. Particularly since polysorbates are included in protein formulations to stabilize the protein, the decrease in the concentration of polysorbate and the accumulation of degradant molecules in a pharmaceutical polypeptide formulation is of potential concern for protein stability.
Numerous molecules targeted at the HGF/c-met pathway have been reported. These molecules include a portion of the extracellular domain of c-met and anti-c-met antibodies such as those described in U.S. Pat. No. 5,686,292, Martens, T. et al., Clin. Cancer Res. 12 (20 Pt. 1):6144 (2006); U.S. Pat. No. 6,468,529; WO2006/015371; WO2007/063816, and WO2010/045345. Bivalent forms of anti-c-met antibodies have been shown to promote dimerization and lead to activation of c-met (agonistic function), while conversely monovalent antibodies have been shown to inhibit c-met activity (antagonistic function). For treatment of pathological conditions requiring an antagonistic function, bivalency of an anti-c-met antibody could result in an undesirable agonistic effect, and therefore, the monovalent trait is required to ensure an antagonistic activity upon binding of the anti-c-met antibody to the target for treatment of the pathological condition. Fab fragments and one-armed antibodies are examples of monovalent antibodies. One-armed antibodies generally have a longer half-life than Fabs. However, as a one-armed antibody comprises a single light chain and a single heavy chain (as well as an additional Fc region), if the one-armed antibody structure is not stabilized, the polypeptides could potentially form a bivalent antibody with two heavy chain and two light chains. Aggregation of monovalent antibodies (formation of multimer and oligomers) and/or failure to maintain monovalent structure in a pharmaceutical formulation comprising anti-c-met antibodies could lead to an undesirable agonistic effect. Minimization of anti-c-met antibody aggregation in the pharmaceutical formulation is thus particularly important. Therefore, despite the significant advancement in the molecules which target the HGF/c-met pathway, stable pharmaceutical formulations, which minimize aggregation of c-met antibodies, are still needed.
All references cited herein, including patent applications and publications, are incorporated by reference in their entirety.